There are lots of electrical apparatuses supplied by batteries, such as handheld electronic devices, cell-driven vehicles, or other apparatuses with built-in batteries; in general, the batteries can serially connect battery modules to form at least one battery module series for supplying the voltage level required by the above-mentioned electrical apparatus. After the above-mentioned electrical apparatus consumes electricity supplied by the battery module series, the conventional charger apparatus charges the battery module series by using one charger; however, the difference in characteristics of different battery modules of the battery module series often causes charging and discharging difference between these battery modules, such as undercharge or overcharge.
Therefore, the charger apparatus not only charges the battery module series but also equalizes the batteries. The conventional charger apparatus includes not only the charger but also a corresponding monitor/equalization circuit (adjustment logic) installed in each battery module of the battery module series to monitor/equalize the charging condition of every battery module and to control matching or equalization of the battery module series. The additional monitor/equalization circuit often increases the cost of the conventional charger apparatus; moreover, the cost of the charger is rather high due to the high charge voltage supply of the charger for charging the battery module series.